The present invention relates to dynamoelectric machines having a rotor that is cooled using forced convection of gases to remove heat from the rotor. It is particularly applicable to high speed machines where the windage loss experienced by the machines is significant.
This invention is an improvement on my Canadian Patent 1,238,933 issued Jul. 5, 1988 and entitled Cooling System with Reduced Windage Loss. My Canadian Patent discloses a sealed rotor dynamoelectric machine having reduced windage loss by having turning vanes at opposite ends of the rotor. One set of vanes is utilized for directing gas into the rotor and another set of vanes for directing the gas from the rotor into adjacent rotary structure for circulation. The rotor has cooling slots defined by the interpolar space between two adjacent poles of the rotor and a shield or cover member placed across the slot to enclose the interpolar space. Any gas directed by the vanes into the slot moves axially along the slot and is prevented by the shield cover from moving radially out the slot, across the air gap and into the stator member surrounding the rotor. As a result, the use of the vanes and the cover shield provide a reduction in windage loss associated with gas flow for cooling the rotor structure
Accordingly there is a need to provide a ventilation system for a dynamoelectric machine wherein windage loss associated with coolant gases entering the rotor interpolar spaces or ducts present a minimal windage loss while at the same time having the advantage associated with the use of interpolar space coolant ducts.
The present invention relates to the cooling of a dynamoelectric machine having a rotor with a shield or cover as disclosed in my previous Canadian Patent 1,238,933 and with the improvement of inlet and outlet shrouds extending radially over opposite radial end surfaces of the rotor. The inlet shroud provides a gas inlet path where rotation of the shroud acts as a pump to accelerate the gas tangentially to have an angular velocity equivalent to that of the rotor at the rotor poles. The inlet shroud then directs the gas into the axially extending interpolar spaces. The outlet shroud covers the other side or end surfaces of the rotor to provide a radially extending outlet path from the rotor poles towards the rotor axis. The outlet shroud acts as a turbine to recover energy from the gas stream as the angular component of velocity of the gas decelerates. As a result, windage loss associated with gas stream flow into and out of the interpolar spaces or ducts is reduced.
Preferably, a blower or pump motor is utilized to direct the gas flow through the rotor in a predetermined direction and to compensate for static pressure losses of the gas moving axially along the interpolar spaces. However, the radial extension of the inlet shroud relative to the outlet shroud may be chosen to optimize windage loss and compensate for static pressure losses. It is envisaged that in some embodiments no external pump or blower is needed to compensate for static pressure losses.
In accordance with one aspect of the present invention there is provided a dynamoelectric machine comprising a stator member and a rotor member mounted within the stator member on an axially extending shaft. The rotor member having spaced apart radially extending first and second end portions and a plurality of spaced apart ventilation ducts each extending between the first and second end portions in a substantially axial direction. The machine comprises a first shroud member mounted to the rotor adjacent the first end portion of the rotor for rotation therewith. The first shroud extends radially over and is spaced from the radially extending first end portion of rotor to define a radial gas inlet path therewith. The first shroud has a first radially inner end portion adjacent to and spaced from the shaft to define a gas inlet and a second radial outer end portion mounted to the rotor for directing gas into the ventilation ducts. The first shroud member rotates with the rotor to angularly accelerate the moving gas along the radial gas inlet path and into the ventilation ducts. The machine includes a second shroud member mounted to the rotor adjacent the second end portion of the rotor for rotation therewith. The second shroud extends radially over and is spaced from the radially extending second end portion of rotor to define a radial gas outlet path therewith. The second shroud has a second radially inner end portion adjacent to and spaced from the shaft to define a gas outlet and a second radial outer end portion mounted to the rotor adjacent the spaced apart ventilation ducts for receiving gas exiting the ventilation ducts. The second shroud member rotates with the rotor to decelerate angularly the gas exiting the ventilation ducts and traveling along the radial gas outlet path.
Preferably, the rotor includes a plurality of spaced apart poles adjacent an air gap with the stator member. Between adjacent poles is defined an axially extending interpolar space and a cover member extends between the poles across the interpolar spaces to define the ventilation ducts. Alternatively, the ventilation ducts may be axial passages in the rotor core.
Preferably the dynamoelectric machine is a sealed rotor dynamoelectric machine. Preferably each of the first and second shrouds has a curved rim surface adjacent respective first and second radially outer ends to redirect gas flow respectively between radial and axial flow, and axial and radial flow. It should be understood that the curved rim may comprise a single metal member bent into a curve or a series of flat pieces angled relative to each other to provide the required curvature.
It is within the realm of the present invention for the dynamoelectric machine to include a blower motor adjacent one of the gas inlet, gas outlet or both to direct gas flow into the gas inlet, along the radial gas inlet path, axially along the ventilation ducts, along the radial gas outlet path and out the gas outlet.
It is also envisaged that the outlet shroud extends radially towards the axis a predetermined distance less than the inlet shroud to create a pressure differential between the gas inlet and gas outlet that causes or facilitate the flow of gas into the inlet, across the rotor and out the outlet.